(1) Field of the Invention
This invention relates to photohardenable imaging compositions and elements useful in the preparation of continuous-tone dye images, such as for color-proofing.
(2) State of the Prior Art
Previous color-proofing elements have contained a coating of a diazo resin in admixture with an inert polymeric binder to provide an anionic mordant which, with a cationic dye, forms a continuous-tone image. One example is illustrated in Canadian Pat. No. 998,278 issued to H. McGuckin, wherein the polymeric binder was hydroxyethyl cellulose. However, in such a system the binder of the coating remains intact as an integral layer even in the unexposed regions. This differs from more conventional systems of photohardenable diazo resins wherein the wash step removes the unexposed coating entirely. The latter system has been called a "wash-off" system to distinguish it from the wash-out systems such as are described in the above-noted Canadian patent.
In the past, wash-off diazo resins have had limited usefulness in color-proofing systems for a number of reasons. First, the speed of such resins by themselves has been somewhat slow. Second, the contrast resulting from the resin in a wash-off system has been such that a continuous-tone image has been difficult to produce therefrom. Graphic Arts Monthly, March, 1967, p. 74, notes, "At present, . . . there is no satisfactory means of proofing continuous-tone separation negatives. Presently available color films have too high a contrast for this use . . . ." Third, the only mordanting that can be achieved from a diazo resin is that of cationic or nonionic dyes, as is shown, for example, in the aforesaid Canadian patent. Much greater dye flexibility would be possible if an anionic dye system can be developed. Other light-sensitive materials have been used with anionic dyes, for example, diazo salts as described in the aforesaid Canadian patent, but diazo resins are preferred over the salts because the resins have a higher speed.
Still other examples exist of light-sensitive elements comprising a layer of light-sensitive polymer which, when photohardened, is used to mordant a dye, including anionic dyes, in the exposed areas remaining after a wash-off step. U.S. Pat. No. 2,887,376 issued to Tupis on May 19, 1959, illustrates examples of such elements, such as quaternized ammonium polymers or certain azido polymers dispersed in acrylate polymers. However, although such elements are highly useful, they do require a dispersion for coating and the use of elevated temperatures and alkaline solutions for the wash step, both of which tend to discourage the formation of continuous-tone imaging.
Continuous-tone color-proofing transfer systems featuring sender and receiver sheets have utilized the immobilization of dye in a colloidal system containing a light-sensitive azide, control of mobility being achieved by control of pH of the sender layer rather than by a mordant. An example of such a disclosure is U.S. Pat. No. 3,598,586 issued on Aug. 10, 1971, to Gaspar. However, pH control is less convenient than a system which internally and automatically fixes the dye.
Mordants of many kinds have been developed for the mordanting of both cationic and anionic dyes in a variety of binders. Patents illustrative of such mordants include U.S. Pat. Nos. 3,958,995 issued May 25, 1976, 3,756,819 issued on Sept. 4, 1973, 3,758,445 issued on Sept. 11, 1973, 2,635,535 issued on Apr. 21, 1953, 2,107,094 issued on Feb. 1, 1938, and 2,063,348 issued on Dec. 8, 1936, and British Pat. Specification Nos. 852,483 published Oct. 26, 1960, 1,245,952 published Sept. 15, 1971, 1,161,128 published Aug. 13, 1969, and 1,277,453 published June 14, 1972.
Patents relating to the background of dye transfer include U.S. Pat. Nos. 1,517,200 issued Nov. 25, 1924, 1,643,529 issued Sept. 27, 1927, and 2,931,296 issued Apr. 5, 1960.
Patents relating to the background of dyes utilized with lithographic light-sensitive materials in general, but not in conjunction with a mordant, include U.S. Pat. Nos. 2,667,415 issued Jan. 26, 1954, to Neugebauer et al, 2,687,958 issued Aug. 31, 1954, to Neugebauer, 3,692,826 issued Oct. 26, 1954, to Neugebauer et al, 3,010,391 issued Nov. 28, 1961, to Buskes et al, and 3,715,210 issued Feb. 6, 1973, to Watkinson et al. Of these, the Neugebauer U.S. Pat. No. 2,667,415 refers to anionic dyes but apparently only in conjunction with the treatment of the exposed foil or base rather than the light-sensitive diazo layer.